(1) Field of the Invention
This invention relates to a converting controller, and more particularly to a converting controller with an active error correction for feedback control.
(2) Description of the Prior Related Art
FIG. 1 is a schematic circuit diagram of a conventional LED driving circuit. The LED driving circuit includes an inductor L, a switch M1, a diode M2, a current detecting resistor Ri, and a converting controller 10. One end of the inductor L is coupled to an input power source Vin, and the other end thereof is coupled to the positive end of the LED module 20. The negative end of the LED module 20 is coupled to one end of the switch M1, and the positive end of the diode M2. Another end of the switch M1 disposed away from the LED module 20 is grounded through the current detecting resistor Ri. The negative end of the diode M2 is coupled to the input power source Vin and the inductor L for freewheeling current.
The converting controller 10 is an integrated circuit, and is usually packaged into a single chip with the pins including a feedback end FB, a power end VD, a driving end DR, a grounding end GD, etc. The power end VD is coupled to a driving power source VDD for accessing operating power. The grounding end GD is grounded. When the switch M1 is conducted, an LED current of the LED module 20 flows through the switch M1 and the current detecting resistor Ri to ground, and a current detecting signal Ifb is generated. The converting controller 10 receives the current detecting signal Ifb via the feedback end FB for determining whether the LED current reaches a predetermined peak value or not. If yes, the switch M1 will be temporarily switched off for a predetermined off time to have the LED current staying between the predetermined peak value and a valley value.
Ideally, the peak value of the LED current should be a fixed value without being changed by the voltage of the input power source Vin or other factors. However, the circuit has a response time delay which will affect a current change slope for various input power sources Vin, and thus the actual current peak varies with the input power source Vin. In addition, the component error in inductance value of the inductor L is quite significant and may change the amount of time delay even under the same application environment. The aforementioned issues will become uncontrollable variables in actual applications.
Thus, it is an important issue desired to be resolved in the field to reduce or even control the influence of error and response time delay between the ideal case and the actual case within an acceptable range.